Computer control system for refining and hydrogenation of unsaturated hydrocarbons

ABSTRACT

Described is a control system for a refining hydrogenation and deodorizing plant for edible oils and the like wherein various system variables are converted into signals which are fed to a computer which controls the system to optimize performance and reduce oil losses.

United States Patent Pufrman [4 1 Apr. 4, 1972 [54] COMPUTER CONTROLSYSTEM FOR [56] References Cited REFINING AND HYDRDGENATION OF NlTEDSTATES P TENTS UNSATURATED HYDROCARBONS U A 2,607,718 8/1952 Southard..260/425 X [721 lnvemofi Richard mma", Plttsbufgh, 2,881,235 4/1959 VanPool ..23/253 A x [73 I Assigneez Westinghouse Electric corporaflon, pu3,413,324 1 H1968 Seip ..260/425 b h, P S mg a Primary Examiner-JosephScovronek Filed! 1969 Attorney-F. H. Henson and R. G. Brodahl [21] Appl.No.: 885,405 [57] ABSTRACT Described is a control system for a refininghydrogenation and [52] U.S.Cl. ..23/253 A, 23/260;23/285, deodon-zingplant for edible oils and the like wherein various 137/88 202/160 25/15260,409 260/425 system variables are converted into signals which arefed to a [51] Int. Cl. "B01 1/00, C1 lb 3/06, GOln 27/00 computer whichcontrols the system to optimize performance [58] Field of Search..23/253, 253 A, 230 A, 260, and reduce oil losses 9 Claims, 3 DrawingFigures CRUDE STORAGE CAUSTIC FEED I6 25 TANK FEED ,2? TANK (H2O) TANKl2 INPUT COMPUTER OUTPUT OUTPUT 92 CENTRIFUGE I TYP HEAT WR'TEREXCHANGER T K VACUUM TANK COMPUTER CONTROL SYSTEM FOR REFINING AND HYDROGlENATION OF UNSATURATED HYDROCARBONS BACKGROUND OF THE INVENTION Ina hydrogenation plant, particularly a hydrogenation plant for edibleoils, the crude oil is initially refined to remove impurities, thenwinterized to remove glycerides which would otherwise crystallize in adomestic refrigerator, then hardened or hydrogenated, and finallydeodorized to remove volatiles together with residual free fatty acids.

The object of refining is to remove the free fatty acids by neutralizingwith a caustic, usually sodium hydroxide, and to remove thephosphatides, proteins or other substances which, after hydration,report to the soap stock in'passing through a centrifuge or separator.The oil is pumped with a proportioned amount of caustic of predeterminedconcentration to mixers in which much of the chemical reaction takesplace. The reactions include neutralization of the free fatty acids andhydration of gums and the like. The resulting material then passesthrough a heat exchanger where the temperature is raised toapproximately 150 F., and then to primary separators in which the gumsand soaps are separated from the neutral oil. The neutral oil,containing traces of sodium and water, then passes through a second heatexchanger to a mixer, into which is also fed heated water together witha small amount of phosphoric acid for the neutralization of any causticcarried over with the neutral oil. This mixed liquid is then pumped tosecondary or washing separators. Here the neutral oil is separated fromthe water and is pumped to a vacuum drier in which any water remainingin the oil is removed.

After winterizing to remove glycerides, the oil is pumped from storageand passes through a heat exchanger where it is heated to approximately250 F. before entering the hydrogenation converter. A catalyst of asuitable grade is slurrified with the oil and pumped into the converter.Hydrogen is then bubbled through the heated oil, in which process theunsaturated oil is converted to a hydrogenated or saturated oil whichwill harden upon cooling. Finally, the oil is processed in a deodorizingvacuum chamber where volatiles are removed and the remaining free fattyacids are recovered.

In the refining process, enough caustic should be added to remove thefree fatty acids and other impurities. However, if too much caustic isadded, it converts the desired oil into a soap which is lost in acentrifuge. In the past, the efficiency of the refining process in termsof oil loss has been determined only at the end of a processing cyclefor a batch of oil. In other words, excessive caustic addition and soapgeneration was determined after the fact when it was too late to correctthe matter for a particular batch.

In a somewhat similar manner, the degree of hydrogenation has heretoforebeen determined after the fact" by taking a sample of the oil anddetermining the iodine value which is linearly related to the amount ofhydrogen absorbed by the oil. No known satisfactory means has beendevised for continually monitoring the amount of hydrogen absorption todetermine the end point of the hydrogenation process.

SUMMARY OF THE INVENTION As an overall object, the present inventionseeks to provide a computer control system for an oil refining andhydrogenation plant whereby the process can be controlled on-line ratherthan by trial-and-error testing techniques.

More specifically, an object of the invention is to provide a means forcontrolling an edible oil refining process wherein the sodium content inneutral oil is measured and continually monitored and the caustic-to-oilflow ratio in the system ad justed to attain elimination of fatty acidsand other impurities without excessive loss of oil due tosaponification.

Another object of the invention is to provide a method for controllinghydrogenation of unsaturated hydrocarbons by a comparison of the massflow rates of hydrogen into and out of a bath of oil to be hydrogenated.

Still another object of the invention is to provide a new and improvedsystem for deodorizing edible hydrogenated oil by elimination ofvolatile materials.

In accordance with the invention, optimization of the refining processis achieved by causing a computer to periodically make a deliberatechange in the caustic-to-oil flow ratio. The computer also measures thecorresponding change in sodium content of the neutral oil, without atthis time making a correcting adjustment to back pressure at the outputof a centrifuge. If the sodium is deficient, only a small change insodium in the neutral oil will be detected since the sodium will reactwith the free fatty acids. If the sodium is in excess, a small changewill again be recorded due to saponification. The largest change willoccur with maximum neutralization of free fatty acids at minimumsaponification of neutral oil. Thus, the computer, by making a series ofsmall changes in the causticto-crude oil ratio first in one direction,then in the other and noting the effect on sodium in neutral oil,adjusting back pressure and repeating the process, can establish theoptimum caustic-to-crude oil ratio for a given crude. By controlling thesodium content in the neutral oil at an agreed low level, the neutraloil recovery rate also will be optimized.

In the hydrogenation process, hydrogen is bubbled through heatedunsaturated oil, most of the gas passing through the oil being pumpedback to the inlet. However, the space above the oil is also connectedthrough a suitable valve to a purge outlet in order to bleed offnitrogen which accumulates above the bath of oil. By measuring thehydrogen content of the purged gas, and from a consideration of the nethydrogen absorbed, the nitrogen content of the purged gas can becontrolled so as to hold it at some maximum level. Furthermore, from aconsideration of the amount of hydrogen fed into the system and thatpurged with the nitrogen, the total hydrogen absorbed can be determinedto determine the end point of the hydrogenation process.

In the deodorizing of the refined oil, the oil is placed within acontainer and a vacuum is created above the oil by means of steamejectors. Completion of the deodorizing process is determined by meansof a total hydrocarbons analyzer which determines the rate of change ofvolatile content in the vapor.

The above and other objects and features of the invention will becomeapparent from the following detailed description taken in connectionwith the accompanying drawings which form a part of this specification,and in which:

FIG. 1 is a schematic diagram of the crude oil refining system forunsaturated oils showing the manner in which it is controlled by meansof a computer in accordance with the invention;

FIG. 2 is a schematic diagram of hydrogenation apparatus for unsaturatedoils showing the manner in which it is controlled by means of a computerin accordance with the invention; and

FIG. 3 is a schematic diagram of an oil deodorizing system showing themanner in which it is controlled by means of a computer in accordancewith the invention.

With reference now to the drawings, and particularly to FIG. 1, thesystem shown includes a computer 10 having input terminals 12 and outputterminals 14. As will be seen, the computer 10 is used not only tocontrol the refining process shown in FIG. 1 but also the hydrogenationprocess of FIG. 2 and the deodorizing process of FIG. 3.

Crude unsaturated oil such as soybean oil, peanut oil, corn oil or thelike is stored in a tank 16 and fed by means of pump 18 to a firstpositive displacement flowmeter 20 and thence to a density meter 22which may be of the weighted U-tube type. The signals from flowmeter 20and density meter 22 are fed to the computer 10 as shown.

After passing through the density meter 22, the crude oil passes througha three-way valve 24, after which water from storage tank 25 and acaustic such as sodium hydroxide from a caustic feed tank 27 is added tothe oil via conduits 26 and 28. The mixture then passes to a mixer 30where much of the chemical reaction between the caustic and free fattyacids as well as hydration occurs. The mixture then passes through aheat exchanger 32 where the temperature is raised to approximately 150F. and then to a first centrifuge 34. The centrifuge 34, which operateson the principle of differential specific gravities, causes the mixtureto rotate whereby the heavier soaps and impurities will be caused toflow radially outwardly while the refined oil remains at the center ofthe centrifuge. The soaps are skimmed off and the refined oil passedthrough valve 36 and three-way valve 38 to a second positivedisplacement flowmeter 40 and a second density meter 42. The flowmeter40 and density meter 42 also produce electrical signals which are fedback to the input of computer 10.

Connected to the conduit carrying the refined oil intermediate theflowrneter 40 and density meter 42 is a flame photometer 44 designed forthe measurement of sodium concentration. The photometer 44, therefore,provides a means for determining whether excess sodium has been added tothe oil. The analyzer 44 also produces an electrical signal which is fedto the input of computer 10.

After passing through density meter 42, the oil passes through a thirdthree-way valve 46 and thence through a heat exchanger 48 to a mixingtank 50 where it is mixed with water and phosphoric acid supplied from astorage tank 52. The phosphoric acid, which is added in only smallamounts, serves to neutralize any residual caustic in the neutral oil.

From the storage tank 50, the oil is pumped by pump 54 to a secondcentrifuge 56. Here the neutral oil is separated from the water and isthereafter pumped to a vacuum drier 58 where any water remaining in theoil is removed. The refined oil is then pumped by pump 60 to a refinedoil tank 62 where it is stored preparatory to its being hydrogenated.

The lye added to the oil from tank 27 consists of sodium hydroxidedissolved in water, the amount of water present varying with sodiumhydroxide concentration. The caustic-tooil flow ratio is a chemicalrelationship determined by the need to neutralize the free fatty acidswithout excessive saponification of neutral oil. The water, on the otherhand, all reports to the soap since only traces are found in the neutraloil. The total amount of water added may, therefore, be regarded as thatrequired to insure a free flowing soap.

In the system shown in FIG. 1, the water and lye flow rates arecontrolled separately; and it is necessary to make up a lye with aconcentration which requires dilution by the on-line addition of water.This means the system must run with a lye concentration slightly higherthan would ordinarily be the case. The water, in passing from tank 25,passes a thermometer 64 and then passes through a flowmeter 66 and avalve 68. An electrical signal proportional to the temperature of thewater is applied to the computer 10, as is the flow rate as determinedby the flowmeter 66. The flowmeter 66 also controls a controller 70 forthe valve 68, the set point for the controller being derived from theoutput of the computer 10.

Likewise, the caustic solution, as it passes from tank 27, first has itstemperature measured by thermometer 72 and then passes through flowmeter74 and valve 76 before it reaches the mixer 30. Signals proportional totemperature and flow rate from elements 72 and Marc applied to the inputof the computer 10, the output of the flowmeter 74 also being usedtocontrol a controller 78 for the valve 76. The controller 78, likecontroller 70, receives the set point signal from the output of thecomputer 10.

Connected to the input and output of the centrifuge 34 are pressuresensing devices 80 and 82. These pressure sensing devices 80 and 82produce electrical signals, proportional to pressure, which are fed backto the input of computer 10. The pressure sensor 82 also serves tocontrol a controller 86 for valve 36, the controller 86 receiving a setpoint signal from the output of computer 10.

It can be seen, therefore, that the computer controls the setting ofvalve 36 as well as the settings of valves 68 and 76 in order to add thecorrect amount of caustic to the oil without excessive saponification ofthe oil due to an excess of sodium.

Neglecting traces of sodium and water in the neutral oil, the recoveryof neutral oil, R, can be calculated as follows:

n' n/ n o' o where G, neutral oil flow as determined by flowmeter 40;

D,, =neutral oil density as determined by density meter 42;

G crude oil flow as determined by flowmeter 20;

D, crude oil density as determined by density meter 22;

and

N.,= neutral oil in crude oil as determined by analysis.

The precision with which this calculation can be carried out dependsupon the accuracy of instrument calibration. If, during a calibrationrun, the same oil under the same conditions is passed through the twosets of flow and density meters (20, 22 and 40, 42) in series, acalibration factor (fa) can be calculated for the ratio G,,/G,, andanother calibration factor (fd) for the ratio D,./D,. Equation I) thenbecomes:

In order to initially calibrate the system of FIG. I, the threewayvalves 24, 38 and 46 are adjusted such that oil from density meter 22flows through by-pass conduit 88 to meters 40 and 42 and thence throughvalve 46 and conduit 90 back to storage tank 16. Under these conditions,the computer 10 calculates the values for (fa) and (I'd). When thevalves 24, 38 and 46 are then returned to the positions shown in FIG. 1and the refining process started, the computer 10 continually calculatesrecovery, R, and prints it out on typewriter 92. This gives the operatoran up-to-date indication of recovery such that if the recovery is toolow, corrective action can be taken immediately instead of waiting untila complete batch of oil has been processed and the weight of the refinedoil compared with the weight of the crude.

The flow rate, F of lye into the mixer 30 can be expressed as 1. 1. 1.where:

G,, the flow rate as determined by meter 74, and

D, K(T Na where K is a constant, T, is the temperature measured bythermometer 72 and Na is the sodium in the lye as NaOH. Na will beinserted into the computer via an operator's console after laboratorytitration of a sample. Thus, by measuring temperature via thermometer72, flow rate via meter 74, and from a knowledge of sodium in the lye,the computer 10 can solve equation (3) above to determine the flow rateof lye into the mixer 30. This is applied as a set point signal to thecontroller 78.

Similarly, the computer can compute the amount of water,

W added with the lye from:

(4) W =F,,(l00-Na /l00) and the amount of dilution water, W added fromtank 25 from:

(5) W,, 62.3 -G K(I,,) where:

G, water flow rate determined by meter 66;

i K a constant; and T, the temperature of the water as determined bythermometer 64.

The pressure transducers and 82 also send signals to the computer 10indicative of the input and back pressures of the centrifuge 34. If theback pressure should increase without a corresponding increase in inputpressure, it is known that more material is reporting as soap stock.

Optimizing of the process is carried out as follows:

The computer can periodically make a deliberate change (increase) incaustic-to-oil flow ratio by adjustment of valve 76 and/or valve 68 andmeasure the corresponding change in sodium content by the sodiumanalyzer 44 without at this time making a correcting adjustment to backpressure via valve 36. As a diagnostic statement, it can be said that ifthe sodium is deficient, only a small change in sodium in the neutraloil will be detected since the sodium will react with the free fattyacids. If the sodium is in excess, on the other hand, a small changewill again be recorded due to saponification. The largest change willoccur with maximum neutralization of free fatty acids and minimumsaponification of the neutral oil.

Thus, the computer, by making a series of small changes in caustic-crudeoil ratio first in one direction. then in the other, and noting theeffects on sodium in the neutral oil, adjusting back pressure via valve36 and repeating the process, can establish the optimum sodiumhydroxide-crude oil ratio for a given crude. All of this, of course, iscontrolled primarily by the reading of the sodium analyzer 44; whilesodium content is varied by controlling centrifuge back pressure via aset point signal to controller 86. As back pressure increases, thesodium content will decrease and vice versa.

With reference now to FIG. 2, the hydrogenation equipment for the crudeoil refined in the process of FIG. 1 is shown. It includes a reactiontank 94 into which a batch of refined oil is poured up to the level 96.At the bottom of tank 94 is a conduit 98 having a plurality of openingstherein which permit hydrogen to bubble up through the oil within thetank. The space above the level 96 in the tank 94 is connected throughconduit 100 and constant displacement pump 102 to the conduit 98. Theconduit 98 is also connected through control valve 104, a density meter106 and a flowmeter 108 to a source of hydrogen under pressure. Thesignals from the density meter 106 and flowmeter 108 are applied to thecomputer shown in FIG. 1.

The conduit 1100 is connected through a second flowmeter 110, a thermalconductivity analyzer 112, a purge valve 114 and a density meter 116 toa purge outlet port. The signals from flowmeter 110, thermalconductivity analyzer 112 and density meter 1 16 are also fed back tothe computer shown in FIG. 1. In the space above the level 96 of the oilin tank 94, nitrogen will accumulate, and it is the purpose of the purgevalve 114 to permit a certain amount of the gas to escape in order toprevent an excessive accumulation of nitrogen above the oil in the tank94. The thermal conductivity analyzer 112 determines the amount ofhydrogen in the purged gas.

The pressure of the gas above the level of the oil in tank 94 isdetermined by means of a pressure transducer 118 which applies a signalback to the computer of FIG. 1. Similarly, the temperature of the oilwithin tank 94 is measured by thermometer 120 which produces anelectrical signal fed back to the computer 10. The signal from pressuretransducer 118 is utilized by the computer to produce a set point signalon lead 122 for a pressure controller 124 which regulates the setting ofvalve 104. The signal from thermometer 120, when fed back to thecomputer 10, provides a set point signal on lead 126 for a temperaturecontroller 128. The temperature controller 128, in turn, controls avalve 130 supplying cooling water to cooling coils 132 within the tank94.

In the control of the hydrogenation process, the amount of hydrogenflowing into the tank 94 is determined from a consideration of the flowrate and density signals produced by meters 106 and 108. The amount ofhydrogen leaving the system is determined by the thermal conductivityanalyzer in combination with the meters 110 and 116. The net hydrogenabsorbed by the oil, therefore, is the difference between the amount ofhydrogen flowing into the system and the amount flowing out; and whenthis amount reaches the desired value for a particular weight of oilwithin the tank 94, the process is stopped. The signals from the thermalconductivity analyzer 112 and the meters 110 and 116 also serve toestablish the setting of valve 114, determining the amount of gas whichis purged from the to of the tank 94. As the amount of hydrogen in thepurged gas decreases, it is known that the amount of nitrogen isincreasing and vice versa.

With reference now to Fig. 3, a deodorizer for the refined oil is shown.It includes a vessel 136 into which a batch of oil is poured. Connectedto the wall of the vessel 136 above the level of oil therein is a steamejector 138 which creates a partial vacuum above the oil in the vessel136. At the bottom of the vessel 136 is a conduit 140 connected to asupply of steam and having openings therein such that steam will bubbleup through the oil. The flow rate and density of the steam fed into thesystem are measured by flowmeter 142 and density meter 144,respectively. The steam output is fed through a total based upon theflame ionization principle.

It is known that the higher the vacuum above the oil in the vessel 136,the shorter is the time required to complete deodorizing of a batch ofoil. The vaporization efficiency of the process is also a function ofthe surface area of the steam bubbles passing upwardly through the oiland the time during which they are in contact with the oil. Thetemperature of the oil is a further factor in the control of theprocess, since it determines the vapor pressures of the components whichare to be removed. The hydraulic head of the oil in the vessel alsoexerts an efiect on the amount of vaporization efficiency.

Oil losses occur by entrainment in the steam exhausted from thedeodorizer vessel and by distillation of the free fatty acids which canbe formed by hydrolysis. In the case of the free fatty acids, therecomes a point where the formation of them by hydrolysis equals the rateof distillation. With regard to entrainment, the higher the steam flowrate, the higher the oil losses. Less steam is, however, required when ahigher vacuum can be obtained.

Both oil losses and deodorizing time are reduced at higher vacuums.However, the capacity of the vacuum generating system to handle vaporsis limited. The amount of vacuum will also vary from time-to-timedependent on the availability and pressure of the steam supplied to theejectors and to the cooling water temperature supplied to the barometriccondensers in the scrubber. This is thus a major constraint on thesystem.

The real check on completion of the deodorizing process is the rate ofchange of volatile content in the vapor. Reaching a low asymptotic valueis an indication that an equilibrium condition has been established andthat no further improvement can be made in the oil by additional time inthe vessel. The operator is advised of this etfect via the totalhydrocarbons analyzer 146 such that the deodorizing process can beterminated and the batch removed.

It is also possible to estimate the total amount of volatiles of alltypes driven off between times t and t, for a constant stripping steamflow. The basic relationship between the total amount of steam, S,required to reduce the volatiles from concentration V to concentration Vis:

S=k1n A/ 8) where k is a function of the total and partial pressures,the vaporization efficiency and the total amount of oil. Thus, if thetotal amounts of stripping steam S and S consumed between times t and tand between times t and t respectively, are known together with thecorresponding amounts of volatiles driven off, V and V then:

+ V From the foregoing equations, the constants k and V can be solved bythe computer. The amounts of volatiles V and V are determined and fedback to the computer by the total hydrocarbons analyzer 146 while thequantities S and S, are determined and fed back to the computer from theelements 142 and 144. Knowing now the quantity V and the desired valueof V,,, the total amount of steam required may be calculated; and,knowing the stripping steam rate, the time required for the volatilesconcentration to fall to the value V can be estimated. As will beappreciated, the computer can then automatically terminate the flow ofsteam at the desired value or can produce an indication such that theoperator can perform this function manually.

Although the invention has been shown in connection with certainspecific embodiments, it will be readily apparent to those skilled inthe art that various changes in form and arrangement of parts may bemade to suit requirements without departing from the spirit and scope ofthe invention.

1 claim as my invention:

1. In a system for controlling a refining plant for edible oils and thelike wherein a caustic solution ismixed with crude oil and the mixturethen passed through a device for separating neutral oil from fatty acidconstituents and soaps formed by saponification of the oil by thecaustic; the combination of means for producing a signal which varies asa function of the caustic content of said neutral oil after extractionfrom said separating device, means for effecting changes in thecausticto-crude oil ratio first in one direction and then in the other,means for electrically analyzing the effect on said signal as said ratiois changed to determine when a maximum change occurs in the signal asthe ratio is changed in one direction and then in the other, and meansresponsive to said analyzing means for controlling said separatingdevice to vary the amount of caustic retained in said neutral oil afterextraction from said separating device until the optimum caustic-tocrudeoil ratio is achieved as indicated by a maximum change in said signal.

2. The combination of claim 1 wherein said analyzing means comprises acomputer.

3. The combination of claim 2 wherein said separating device comprises acentrifuge, a valve in an outlet conduit for neutral oil from saidcentrifuge for controlling the back pressure on said centrifuge, andmeans coupled to said computer for controlling said valve as a functionof the magnitude of said signal.

4. The combination of claim 3 including means for producing electricalsignals which vary as functions of the pressure on the input side ofsaid centrifuge as well as the back pressure on the output side, saidvalve being controlled as a function of the magnitude of saidfirst-mentioned signal as well as said lattermentioned signals.

5. The combination of claim 2 wherein said caustic is added to the oilalong with a controlled amount of water, the computer including meansfor computing the amount of water and caustic to be added.

6. The combination of claim 5 including means responsive to an outputfrom said computer for controlling the amount of water and caustic to beadded to the oil.

7. The combination of claim 1 wherein said means for producing a signalwhich varies as a function of the caustic content of said neutral oilafter extraction from said separating device comprises a flamephotometer.

8. In a system for controlling a refining plant for edible oils and thelike wherein a caustic solution is mixed with crude oil and the mixturethen passed through a device for separating neutral oil from fatty acidconstituents and soaps formed by saponification of the oil by thecaustic; the combination of first means for producing electrical signalsindicative of the mass flow rate of oil before it is mixed with saidcaustic, second means for producing electrical signals indicative of themass flow rate of oil after it passes through said separating device,computer means responsive to said electrical signals for computing theratio of oil leaving the separating device to oil entering saidseparating device from a consideration of said mass flow rates beforeand after passage through said separating device, and means coupled tosaid computer means for printing-out said ratio.

9. The combination of claim 8 wherein the first means comprises aflowmeter and a density meter and said second means also comprises aflowmeter and a density meter.

2. The combination of claim 1 wherein said analyzing means comprises acomputer.
 3. The combination of claim 2 wherein said separating devicecomprises a centrifuge, a valve in an outlet conduit for neutral oilfrom said centrifuge for controlling the back pressure on saidcentrifugE, and means coupled to said computer for controlling saidvalve as a function of the magnitude of said signal.
 4. The combinationof claim 3 including means for producing electrical signals which varyas functions of the pressure on the input side of said centrifuge aswell as the back pressure on the output side, said valve beingcontrolled as a function of the magnitude of said first-mentioned signalas well as said latter-mentioned signals.
 5. The combination of claim 2wherein said caustic is added to the oil along with a controlled amountof water, the computer including means for computing the amount of waterand caustic to be added.
 6. The combination of claim 5 including meansresponsive to an output from said computer for controlling the amount ofwater and caustic to be added to the oil.
 7. The combination of claim 1wherein said means for producing a signal which varies as a function ofthe caustic content of said neutral oil after extraction from saidseparating device comprises a flame photometer.
 8. In a system forcontrolling a refining plant for edible oils and the like wherein acaustic solution is mixed with crude oil and the mixture then passedthrough a device for separating neutral oil from fatty acid constituentsand soaps formed by saponification of the oil by the caustic; thecombination of first means for producing electrical signals indicativeof the mass flow rate of oil before it is mixed with said caustic,second means for producing electrical signals indicative of the massflow rate of oil after it passes through said separating device,computer means responsive to said electrical signals for computing theratio of oil leaving the separating device to oil entering saidseparating device from a consideration of said mass flow rates beforeand after passage through said separating device, and means coupled tosaid computer means for printing-out said ratio.
 9. The combination ofclaim 8 wherein the first means comprises a flowmeter and a densitymeter and said second means also comprises a flowmeter and a densitymeter.